You're Japanese Knife will never be the same

G

gooi

Joined
May 3, 2025
Messages
3
Hi All
I wish to put it out there that for most of us our fancy Japanese knives deteriorate geometrically from the first sharpening. Thinning does not renew our knives but rather attempts to replicate what was once an astonishing cut. That concave bevel is lost as we make our way up the knife. I've tried thinning and that blade road that was once a bowl is gone within a year.
If anyone can suggest a way to get back to the pristine geometry I would love to hear.
 
I think there are a lot of people here that can improve the geometry and make the knife much sharper. With me, it’s a work in progress, but I’m getting there.
 
A Radius platen on a belt sander will put in the shallow hollow grind again. Or a large diameter (like 3-4') and wide stone wheel. If you do it before you lose the concave, it will help keep the concave even since you have a "groove" to follow.

Other Japanese knives are just very thinly ground and convexed; those are easier to keep working like new!

I try to do a Takeda like grind where the upper portion of the blade is hollow ground and the lower portion going to the edge itself is convex.
k tip mc s grind.jpg
 
Most of the knives I am familiar with the hollow in the blade road is left there because it is less grinding and fine scratches are hid by a fake Kasumi finish, it's economics.

No need for a knives performance to suffer at all or to regrind a hollow. Just raise the shinogi line to keep it thin behind the edge as you see fit.

Raise the shinogi up to high and food release will suffer, edges could get to thin ect, so make changes gradually.
 
gooi, there are shops that specialize in sharpening and thinning Japanese style knives.
That might also be a good option for you.
 
gooi said:
Hi All
I wish to put it out there that for most of us our fancy Japanese knives deteriorate geometrically from the first sharpening. Thinning does not renew our knives but rather attempts to replicate what was once an astonishing cut. That concave bevel is lost as we make our way up the knife. I've tried thinning and that blade road that was once a bowl is gone within a year.
If anyone can suggest a way to get back to the pristine geometry I would love to hear.
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Jeeeezzz
I take so little off a knife when I touch up the edge I am sure I will never need to fuss .
I make box knife blades last for years . . .
One of the advantages of an Edge Pro Apex ; just a couple of touches with a couple of stones and hair whittling again .
Never chipped one yet ; that might be a reason for fuss . . .
My Little Monster (as I call my favorite) hangs on the very side of the skin of an apple , tomato or grape. That's pretty acute geometry .
 
gooi said:
most of us our fancy Japanese knives deteriorate geometrically from the first sharpening
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How much steel are you taking off for this to be true?
And my experience with Japanese smiths is that their blades improve a lot with the first sharpening, as they leave finish sharpening to the buyers.
 
With a German knife when you take it out of the box it's the sharpest most users will ever have with it. Japanese knives are generally expected to be sharpened by the end user. In decades of using Japanese knives I only ever found one I couldn't get sharper than new (and that was a custom that had been hand sharpened by a sword polisher in Japan before being sent to me).
 
The OP wasn't complaining about his knife being dull rather losing the hollow of his blade road due to thinning. He just doesn't understand why it was left that way in the first place.
I suppose an argument could be made for it aiding in food release (not by me), those hollows don't last long on my knives, I can't wait to get rid of it.
 
garry3 said:
The OP wasn't complaining about his knife being dull rather losing the hollow of his blade road due to thinning. He just doesn't understand why it was left that way in the first place.
I suppose an argument could be made for it aiding in food release (not by me), those hollows don't last long on my knives, I can't wait to get rid of it.
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Yes
But I would add again that the profile will never be the same wether you like it or not. Thinning does not bring you back to the incredible edge geometry from day one. My point is that so many lauded knives will end up ordinary with use.
 
I know we are taking a particularly small slice of the population here. Could anyone post pictures of their geometry from out of the box to 10 sharpens or so with thinning on stones?
 
FWIW not all Japanese knives are hollow ground on a wheel. There are many different types of knives and manufacture. Some are double bevel, some are single bevel. Some are hand forged and some are made with very high tech cutting, stock removal and laminating. Even the ones that are ground on wheels are often hand sharpened on flat stones before being shipped.
 
The small hollow grind made by the 3 ft. wheel is not of geometric perfection. It is simply the tool of the trade in that part of the world for rough grinding a blade. The quality of this grind can also vary greatly depending on the skill of the maker. Anything from, perfectly clean lines and a grind so flat the hollow is barely noticeable on stones. To, so bad they will tape it off and sand blast it for that "kasumi" finish... these blades are also a nightmare to thin.

Trying to bring back the small hollow is not only pointless but not the correct way of maintaining a Japanese Blade. To thin, you will grind it flat on a stone and work out any hollow in the blade. However, this is not a task for a novice and will require a few more stones than normal so it doesn't look like a mess in the end. Using the correct stones is also important, incorrect stone choice can cause lots of unwanted scratching and distortion of the shinogi line.

Personally, I would be more concerned with behind the edge thickness as the main goal in thinning.
 
I used a Blue #2 carbon gyuto (Tanaka Sekiso, convex ground) in my kitchen at home daily on a wood end grain board to prep for me and my family. I sharpened it on stones (Bester 1200/Rika 5K) at the beginning and stropped it 3 times in the next 9 months, using a balsa strop with 1 micron CBN on it. Maybe 20-30 strokes per side each of the 3 stropping sessions. After I stropped, it would still stick into the cutting board and didn't need to go back to the stones. I only went back to the stones on it after 9 months because I acid etched the blade, which killed the edge. Would have definitely gone longer with just stroppings!

10 sharpenings on stones for me would be over 10 years worth of use in a home cooking setting, but blue #2 is not known for it's edge holding compared to other steels! Unless you are chipping your knife a lot, or resetting the bevel every time you sharpen, you shouldn't be removing a ton of metal each time you sharpen. Stropping on your finest stone or leather and doing routine touch ups should preserve the factory geometry quite a while. When it doesn't perform as well, drop your angle back on your coarsest stone a bit and thin the shoulder area out just behind the edge bevel. Without a micrometer and the pictures taken at the same distance, it would be very difficult to get pictures to compare how it changes over 10 sharpenings.

If you are needing to sharpen enough that you are removing that much metal that quickly, something isn't right. Either go with a more wear resistant steel, or get a way to maintain/touch up the edge without using coarser stones. You should be able to strop a Japanese kitchen knife back to sharp several times before needing to go to the stone and you don't need to start with the coarser stones, either. I have friends who use Konosuke Fujiyama's for several years in a kitchen as their job before they need thinning out again.

With the shallow hollow grind in the main blade bevel, this helps keep the edge thin behind the edge, even with several sharpenings before it thickens up, too, so you will really need to remove a lot of steel to notice a major change in performance.

A friend sent me his buddies Shibata, which are known for being thin lasers and cutting very well. He had chipped it in several places, so I removed the chips (around 3/32" deep or so) and thinned out the area above the new edge a bit and the customer told me it performed better than before! So just because you change the geometry, doesn't mean that the performance is decreased!
 
If you're taking that much steel off of a good knife, I'd argue you're doing something very wrong.
 
toker said:
If you're taking that much steel off of a good knife, I'd argue you're doing something very wrong.
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Would you argue against the practice of maintenance thinning or stone polishing, or are you unfamiliar with them?
 
Mr.Wizard said:
Would you argue against the practice of maintenance thinning or stone polishing, or are you unfamiliar with them?
Click to expand...
I use a Wicked Edge. I match the original edge and go from there. For all of my Japanese knives, I go from 200 grit to 1000 grit. I write down the original angle mearured with an angle cube when I first sharpen the knife. Then I check it with an angle cube from time to time to make sure that the angle has not changed over time.
 
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I've used Japanese knives exclusively in the last 20 years of my chef career. Hardly any of them have ever needed to be thinned. Partly it's probably because I have a stable of about fifteen knives that I rotate though. Between spreading the wear and the fact that the bulk of them utilize superior steel with superb edge retention means they don't need frequent sharpening. And when I sharpen them I take care to remove the minimum amount of steel required to bring the back to razor sharpness. On the other hand, I wind up thinning German/German-style knives quite a bit in my shop. They're often steeled several times per day and often not sharpened with a lot of care or skill (I'm generalizing of course).
 
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